(function () {
  /*---------------------
  --------- API ---------
  ----------------------*/
  class ObjectManager {
    /**
     * this module is responsible for doing hitTesting, like returning the units on certain clicked coordinates or when objects or areas
     * collide with each other.
     *
     * @namespace flatworld
     * @class ObjectManager
     * @constructor
     * @todo It might be a good idea to make the hitDetection more extensive. Now it just uses point or rectangle / bounds to detect hits.
     * It could use sprites or forms.
     */
    constructor() {}
    /**
     * Retrieve objects under certain coordinates or area, if size is given. Uses subcontainers when used, no other options yet.
     *
     * @method retrieve
     * @param {Object} allCoords                                The coordinates which we want to hitTest
     * @param {x:Integer, y:Integer} allCoords.globalCoords     Global coordinates on static layer / canvas
     * @param {x:Integer, y:Integer} allCoords.globalCoords.x
     * @param {x:Integer, y:Integer} allCoords.globalCoords.y
     * @param {Object} allCoords.localCoords                    Local coordiantes on movable layer
     * @param {x:Integer, y:Integer} allCoords.localCoords.x
     * @param {x:Integer, y:Integer} allCoords.localCoords.y
     * @param {string} type                                     type of the object / layer that we want to retrieve
     * @param {Object} options                                  optional options
     * @param {Array} options.subcontainers                     The subcontainers we match against
     * @param {Object} options.size                             Size of the rectangle area to match against, if we want to match rectangle
     * instead of one point
     * @param {Integer} options.size.width
     * @param {Integer} options.size.height
     * @return {Array}                                          matched objects
     *
     * @todo add checks for rectangles. Now we can only check with width = 0 && height = 0
     */
    retrieve(allCoords, containers = [], options = { type: undefined, size: { width: 0, height: 0 } }) {
      var { size, type } = options;
      var { globalCoords } = allCoords;
      var foundObjs = [];

      if (containers.length > 0) {
        containers.forEach(container => {
          foundObjs = foundObjs.concat(container.children);
        });

        if (!size.width || !size.height) {
          foundObjs = filterChildren(globalCoords, foundObjs, type);
        }
      } else {
        return [];
      }

      return foundObjs;
    }
  }

  window.flatworld.ObjectManager = ObjectManager;
})();

function filterChildren(globalCoords, children = [], type = undefined) {
  return children.filter(obj => {
    if (type && type !== obj.type) {
      return false;
    }

    const isHit = obj.hitTest ? obj.hitTest(globalCoords) : true;

    return isHit;
  });
}